Producing the desired result (9)
I believe the answer is:
effective
'producing the desired result' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for effective that I've seen before include "Efficacious, efficient" , "Producing the desired change or result" , "Having the power to produce the desire result" , "Successful in producing the intended result" , "Striking" .)